Beginning with a bilious toast and ending with a group hug, Lynn Shelton's Your Sister's Sister, her fourth film, expertly makes us squirm for about half its running time only to soothe us with empty pop-psych declarations. In Shelton's previous feature, the bolder Humpday, two straight guys, in a moment of perverse macho posturing, agree to do it with each other on camera, but Your Sister's Sister loses interest in the sexual awkwardness and anxiety and uncomfortable truths it sets up. The conclusion suggests a final act Aline Brosh McKenna might have written after scanning headlines about "alternative families."
The sanctity of nuclear bonds — and of the dead — is upended in the opening scene, as friends gather to share warm remembrances of Tom, who died a year ago. As Al (Mike Birbiglia) recounts his pal's altruism, Tom's brother, Jack (Mark Duplass, one of Humpday's dare-taking hets), interrupts the love-in to speak acidly of his sibling as a "bully" and "manipulative." Alarmed by this outburst, Iris (Emily Blunt), a friend of Jack's and a former girlfriend of Tom's, insists that Jack get some "head space" at her father's cabin in the San Juan Islands, off the coast of Washington state.
Vaguely un- or underemployed by choice — there is a mention of "not taking that Trinity job" — Jack pedals his red 10-speed to the idyllic spot, only to find Hannah (Rosemarie DeWitt), Iris's half-sister, in the house, self-medicating with tequila after leaving her girlfriend of seven years. Their judgment impaired by alcohol and grief, the cabinmates have abysmal 90-second sex — an act that they conceal from Iris, who shows up unexpectedly the next day, and one that turns out to have been more than just a silly indiscretion.
With each character hiding a secret — Iris confesses to Hannah that she's in love with Jack — the dialogue in Your Sister's Sister is often a funny combination of stammers, overexplaining, and nervous backtracking. Yet the anodyne-by-design talk often gives way to lacerating revelations. "There'll be no talking behind anyone's back in this house," Jack, too eager to be the perfect guest after Iris arrives, pointlessly says after breakfast one morning. When two members of the triangle aren't waiting for the third to leave the room, the trio will attack in the open. During dinner, Hannah brings up a mortifying boyfriend from Iris's past; Iris retaliates by asking her vegan sibling if she liked the butter she put in the mashed potatoes.
In these moments, the largely improvised script (Shelton credits her leads as "creative consultants") works well, exposing the jabs and parries of passive-aggressive behavior. It all begins to unravel — rapidly and inexorably — however, after a ludicrous confession by Hannah (who, of the three, is saddled with the most clichés, the vegan-lesbian-who-paints, as creaky a character as a Radclyffe Hall heroine).
From there, Your Sister's Sister becomes another movie entirely, filled with montages of sororal cuddles and restorative walks in the woods, and a regressed man's epiphany in a diner — a "healing" arc nearly indistinguishable from that found in nearly every comedy hybrid playing in multiplexes. This softening is all the more disappointing (and puzzling) when compared with Humpday's closing scenes, which were ambiguous, discomfiting, and messy, just like the two characters at its center. As Alex Ross Perry's The Color Wheel — another micro-budgeted sibling story — shows, a film about relentlessly repellent characters is much more fascinating, if not courageous, than one that tries to explain, redeem, or forgive them so easily.